Under tensile loading there is some evidence to suggest that the slope of the S–N curve for stress relieved joints may be slightly higher than for as–welded specimens, and that the endurance limit may be increased ( Gurney, 1979b). Whilst there are other valid reasons for PWHT, for example, to ensure dimensional stability is retained during service, or to provide a reduced risk of brittle fracture, PWHT will seldom provide any benefit in terms of fatigue strength. Post weld heat treatment (PWHT) of welded fabrications is sometimes carried out in the belief that it will provide an improved fatigue performance.

Booth, in Welding in Energy-Related Projects, 1984 THE INFLUENCE OF STRESS RELIEF Read more Navigate DownĬOMMON MISCONCEPTIONS IN THE FATIGUE DESIGN OF WELDED STEEL JOINTS However, PWHT does not make the fatigue performance of the joint any worse, and it may be carried out for other reasons such as dimensional control, improving fracture performance, or prevention of hydrogen cracking. If a tensile residual stress of, say, 100 MPa, remains after PWHT, almost all applied fatigue cycles (assuming these are typically less than 100 MPa in stress range) still result in entirely tensile stresses at the weld toe and are fully damaging.Īs the whole applied stress cycle is almost certainly still tensile, fatigue design codes do not recognise any benefit in terms of fatigue life and require the same design approach to be used for as-welded and PWHT joints. It does not reduce these levels to zero, however, and, even in a very well controlled thermal cycle, the levels of final residual stress are unlikely to be much below 30% of the material yield strength. Post-weld heat treatment (PWHT) reduces the levels of tensile residual stresses in a joint. Philippa Moore, Geoff Booth, in The Welding Engineer�s Guide to Fracture and Fatigue, 2015 13.4.2 Post-weld heat treatment Improving the fracture performance and fatigue life of welded joints

Pwht post weld heat treatment